Glaucoma is one of major eye diseases. Glaucoma is a group of progressive diseases which results in damage to the optic nerve and vision loss. Glaucoma is a multifactorial disease, and subdivision of disease conditions and individualization of treatment are desired. Therefore, various tests and examinations are utilized for diagnosis of glaucoma, such as intraocular pressure examination, corner angle examination, fundus examination (e.g., degree of cupping of optic nerve head, defect of retinal nerve fiber layer, presence or absence of optic nerve head hemorrhage, presence or absence of circumpapillary chorioretinal atrophy), visual field test, image analysis (e.g., optic nerve head shape analysis, layer thickness analysis, lamina cribrosa analysis).
There are classifications according to the shape of the optic nerve head (referred to as optic nerve head shape classification) as the classification methods of the pathology of glaucoma. Classification by Nicolela et al. (referred to as Nicolela's classification) is one of the representatives of such classifications. Nicolela's classification defines four types according to the shape of optic nerve head, namely, focal ischemia (FI) type, myopic (MY) type, senile sclerotic (SS) type, and generalized enlargement (GE) type. The focal ischemia (FI) type is a type in which a notch exists on a part of the rim and a local defect in the optic nerve fiber layer is observed. The focal ischemia (FI) type is often found in females and often accompanied by migraine and stroke. The myopic (MY) type is a type in which the optic nerve head is tilted and crescent shaped peripapillary chorioretinal atrophy (PPA) accompanied by temporal cupping is observed. The myopic (MY) type is often found in younger generation and often accompanied by myopia. The senile sclerotic (SS) type is a type in which the optic nerve head is of circular shape, cupping is shallow, and halo is observed around the optic nerve head. The senile sclerotic (SS) type is often found in the elderly and often accompanied by cardiovascular disorders. The generalized enlargement (GE) type is a type in which a large deep circular cupping is exhibited. The generalized enlargement (GE) type is often accompanied by high intraocular pressure.
Typically, a doctor performs optic nerve head shape classification by interpreting a fundus image acquired using a retinal camera or a scanning laser microscope (SLO). In other words, the classification is performed by the subjectivity of the doctor. Meanwhile, automation of the classification is desired in view of the relatively high prevalence rate of glaucoma and the importance of early detection.
However, the image quality of fundus images obtained by retinal cameras or SLOs is greatly affected by photographing conditions etc. Therefore, quantification of optic nerve head shape parameters is difficult, which is one of the factors that prevents the automation of the classification.
The conventional classification refers only to fundus images (i.e., refers only to the optic nerve head shape parameters) and thus, it is difficult to perform classification with favorable accuracy and precision. On the other hand, although various kinds of ophthalmic information to be referred to is available for classification, considering all of them makes the processing complicated and enormous and the scale and resources of the processing system extremely large. Therefore, putting it into practice is supposed to be difficult.
The followings are examples of publications that disclose related conventional techniques: Japanese Unexamined Patent Application Publication No. Hei10-155744; Japanese Unexamined Patent Application Publication No. 2000-245700; Japanese Unexamined Patent Application Publication No. 2005-253796; Japanese Unexamined Patent Application Publication No. 2006-263127; Japanese Unexamined Patent Application Publication No. 2007-252707; Japanese Unexamined Patent Application Publication No. 2008-220617; Japanese Unexamined Patent Application Publication No. 2008-237839; Japanese Unexamined Patent Application Publication No. 2008-237840; Japanese Unexamined Patent Application Publication No. 2011-83555; Japanese Unexamined Patent Application Publication No. 2016-2380; Japanese Unexamined Patent Application Publication No. 2016-187475; and, Nicolela M T, Drance S M, “Various glaucomatous optic nerve appearances: clinical correlations”, Ophthalmology, Volume 103, Issue 4, April 1996, Pages 640-649